The present embodiments relate to fluorescent compositions such as solid phase change or hot melt inks, and more particularly to a security ink including two fluorescent materials therein which may be activated under different excitation wavelengths to authenticate security documents.
There are many applications in which it is desirable to incorporate a security feature into a document or article. Such security features provide ways to authenticate or validate the article and thus prevent counterfeiting. Security printing capability has been recently enabled for phase change inks. Inks containing a special fluorescent security materials were demonstrated to emit bright colored light when viewed under UV light. The appearance and disappearance of the printed ink upon exposure to radiation feature enables authentication of printed materials (See U.S. Pat. No. 7,674,326 issued on Mar. 9, 2010). Furthermore, the use of encrypted information with fluorescent materials has been demonstrated in (See U.S. Pat. No. 7,549,592 issued on Jun. 23, 2009)
Fluorescent phase change inks enable authentication of documents has been known in the art. Such fluorescent phase change inks are prepared by including a fluorescent dye or a mixture of fluorescent dyes to achieve a desired emitted color under UV light excitation. Prints made with such security inks are typically authenticated with a black light source (UVA). For example, modern currency bills contain a security strip imbedded into them that glows bright green under a black light. A duplicated print can be detected if the counterfeiter finds a fluorescent material emitting the color of the original document when exposed to UV light. However, the short side of this technology is that the final emitted color stays the same (i.e., emits only one given color at different wavelength excitations), which makes such prints vulnerable to counterfeiting as the counterfeiter only needs to match one emitted color.
Thus, there is a need to enhance the security of printed documents. There is a need to provide a cost effective security ink and detection method which is more difficult to counterfeit when compared with the current technology. It is also more beneficial if the ink has properties which a counterfeiter does not expect.
Each of the foregoing U.S. patents and patent publications are incorporated by reference herein. Further, the appropriate components and process aspects of the each of the foregoing U.S. patents and patent publications may be selected for the present disclosure in embodiments thereof.